Conventionally, for an air flow measuring device that measures a flow rate of intake air drawn into an internal combustion engine (may hereinafter be referred to as an intake air amount), for example, there is known a device that employs a thermal-type measuring method whereby a signal is produced in accordance with the flow rate by use of heat transfer between the device and the air. This air flow measuring device includes the following housings and sensor. The housing is disposed to project into an intake passage leading to the engine, and defines an internal passage which takes in a part of intake air flowing through the intake passage and through which the taken-in air passes. The sensor projects into the internal passage, and produces a signal according to the intake air amount by heat transfer between the sensor and the intake air passing through the internal passage.
There is a demand on the air flow measuring device for attachment of a sensor for detecting temperature, humidity and so forth of intake air separately from the sensor disposed in the internal passage (the sensor disposed in the internal passage to produce a signal according to the intake air amount is hereinafter referred to as a first sensor, and the sensor attached separately from the first sensor for detecting temperature, humidity and so forth of intake air is hereinafter referred to as a second sensor). Accordingly, there is proposed a structure that produces a signal by exposing a sensing part of the second sensor directly to the flow of intake air outside the housing.
Because of a cost advantage, employment of a component with a lead wire is considered for the second sensor. For this reason, there is studied a configuration whereby a hole communicating with the inside and outside of the intake passage is provided for the housing, and the lead wire is pulled out of the intake passage with the sensing part remaining disposed in the intake passage, or the lead wire and a rod-shaped conduction body are conductively joined together and the conduction body is pulled out of the intake passage with a conductively joining part between the lead wire and the conduction body, and the sensing part remaining disposed in the intake passage.
The lead wire or the conduction body pulled out of the hole, and a terminal are conductively joined together, and the hole is filled up with a material having a low modulus of elasticity such as silicon to prevent the intake air from leaking out (the hole for pulling the lead wire or the conduction body out of the intake passage is hereinafter referred to as a lead hole, and the material having a low modulus of elasticity with which the lead hole is filled up for the leak prevention of intake air is hereinafter referred to as a filler material. In addition, the lead wire and the conduction body may be collectively referred to as a lead wire or the like).
Moreover, in the air flow measuring device, the terminals are conductively joined together outside the housing to configure a circuit including various kinds of elements of the first sensor. Accordingly, there is known a technical idea of use of injection-molding which gives a cost advantage for providing a mold part for sealing a conductively joining part between the terminals (see, e.g., JP2013-104759A). In case of the attachment of the second sensor, use of injection-molding for sealing a conductively joining part between the lead wire or the like and the terminal may similarly have a cost advantage.
However, when the conductively joining part between the lead wire or the like and the terminal is sealed by injection-molding from resin fluid, high injection pressure is applied to the filler material, so that the filler material may not resist the injection pressure. Therefore, in sealing the conductively joining part between the lead wire or the like and the terminal, it is necessary to prevent or alleviate the application of the injection pressure to the filler material in order to employ injection-molding having a cost advantage.